Marcelo Igor Lourenço

Parameter determination of double-ellipsoidal heat source model and its application in the multi-pass welding process

The parameters of the heat source model have significant influence on the temperature field and sequentially affect the residual stress field. In this paper, a neural-network programme based on the Levenberg–Marquardt algorithm is developed to predict the parameters of Goldaks double-ellipsoidal heat source model. The analytical solution of the heat conduction equation based on the double-ellipsoidal heat source is obtained by integrating a series of instant point heat sources over the volume of the ellipsoidal heat source. The transient temperature distribution and the sizes of the molten pool are obtained under various welding processes by using the analytical method. Then, a neural-network programme is employed to train and predict the heat source parameters. These results of temperature and molten pool size obtained by the numerical simulation with the predicted heat source parameters are calibrated by the published experimental results. The numerical results show a good agreement with the experimental measurements. Finally, the developed Levenberg–Marquardt neural network is employed to predict the heat source parameters in the multi-pass welding process in the laboratory. By comparing the finite element (FE) numerical results with experimental results, the heat source parameters have been successfully identified in the multi-pass welding process.

Development and Experimental Calibration of Numerical Model Based on Beam Theory to Estimate the Collapse Pressure of Flexible Pipes

The constant advance of offshore oil and gas production in deeper waters worldwide led to increasing operational loads on flexible pipes, making mechanical failures more susceptible. Therefore, it is important to develop more reliable numerical tools used in the design phase or during the lifetime to ensure the structural integrity of flexible pipes under specific operating conditions. This paper presents a methodology to develop simple finite element models capable of reproducing the behavior of structural layers of flexible pipes under external hydrostatic pressure up to collapse. These models use beam elements and, in multi-layer analyses, include nonlinear contact between layers. Because of the material anisotropy induced by the manufacturing process, an alternative method was carried out to estimate the average stress-strain curves of the metallic layers used in the numerical simulations. The simulations are performed for two different configurations: one where the flexible pipe is composed only of the interlocked armor, and another considering interlocked armor and pressure armor. The adequacy of the numerical models is finally evaluated in light of experimental tests on flexible pipes with nominal internal diameters of 4 and 6 in.Copyright

Sandwich Pipe: Reel-Lay Installation Effects

Comprising an annular layer with adequate thermal insulation and structural resistance material enclosed by two concentric steel pipes, sandwich pipes could be an alternative for flowlines in ultra-deepwater for the pre-salt reservoirs in offshore Brazil. In this work, a numerical and experimental study was performed to investigate the collapse behavior of sandwich pipes considering the reel-lay installation method. Experimental models were manufactured using two different geometries of stainless steel pipes and strain hardening cementitious composites with PVA fiber (SHCC) in annular layer. One set of specimens was tested using a reel-lay apparatus and another set was kept intact. A hyperbaric chamber was then used to test both sets of specimens to collapse. The collapse resistance of the proposed sandwich structure was investigated, and the detrimental effect of the reeling strains to the collapse resistance was assessed. The numerical models simulated reeling and straightening loads during reel-lay installation and then the collapse under external pressure. The results were compared with experimental measurements and shown good agreement.Copyright

Effect of material model on residual stress and distortion in T-joint welding

ABSTRACT Welding-induced residual stress and distortion have detrimental influences on the ultimate strength of ships and offshore structures. Various experimental and numerical studies have been performed to understand the mechanism of residual stress and distortion under different factors, such as boundary condition, welding sequence and so on. In the present study, experimental tests and numerical simulations were performed to investigate the welding-induced residual stress and distortion under different material models. A sequentially coupled thermo-mechanical finite element model which implemented high temperature effects, temperature-dependent material properties and a moving volumetric heat source was developed to investigate the effect of material model on the residual stress and distortion in T-joint welds. The finite element models were validated carefully by the experimental tests. The results show that the material model has significant effects on residual stress and distortion. Considering that the welding process involves substantial plasticity, the material model must be carefully calibrated.

Modeling for the Optimization Evaluation of Layout Scenarios of Subsea Cluster Manifolds Considering Three Connection Types

Based on a connection matrix and a cost matrix, a mathematical model is presented to describe the optimization evaluation of the layout scenarios of subsea cluster manifolds in ocean engineering at the lowest cost. The connection facilities are considered, including jumpers, pipeline end terminations (PLETs), and infield flowlines. The dedicated series-iteration algorithms programed by MATLAB are conducted to solve this complex nonlinear 0‐1 programming problem. Additionally, numerical simulations are performed to demonstrate the validity of the model and the performance of its algorithms. The results show that the proposed model can precisely describe the layout characteristics of cluster manifolds in engineering and the dedicated algorithms are quite robust. Possible layout scenarios with three-to-eight cluster manifolds for 22 subsea wells can be obtained, from which the optimal one with the lowest cost can be found by comparison. This approach can provide quantitative and efficient references to engineers to assist them in making their decisions in the layout of subsea production systems.

Fatigue Life Assessment of Reeled Risers

One of the most effective installation methods of metallic risers is the reel-lay process, in which pipe segments are welded onshore and subsequently bent over a cylindrical rigid surface (reel) in a laying vessel. During installation, the line is unreeld, straightened, and then laid into the sea under tension. In this process, material properties change and eventual weld defects may increase, thus reducing the fatigue life of those joints under operational loads. Therefore, welded joints must be manufactured based on strict weld acceptance criteria. These criteria shall guarantee reliable standards regarding the fatigue life of the joints while not impairing the feasibility of weld manufacture (high cost). In this work, the reeling process is initially simulated through a nonlinear finite element model that incorporates weld defects. The results are then used as guidelines to experimentally obtain fracture mechanics parameters of typical weld under pre-strained conditions. The fatigue life of as-welded and reeled joints with different defects (lack of fusion and lack of penetration) are subsequently estimated via a finite element model that accounts for the changes in the material properties due to prestraining. The results are compared and used to suggest guidelines to design of reeled steel catenary risers.

Preliminary Design of Floating Point Absorber Offshore Rio de Janeiro

The Rio floating point absorber (FPA) is designed for a reference site located near an island offshore Rio de Janeiro. According to the reference site characteristics, a two-body floating point absorber concept design is chosen to convert ocean wave energy into electrical power. An innovative procedure aiming at finding an optimal shape adapted to predefined wave climate conditions, using the Design of Experiments (DOE) method, is applied. A simple linear damper model is used to represent the Power Take-Off (PTO) mechanism. The optimization procedure is divided into Buoy and support (spar/plate) steps, so the optimized buoy is determined first and then a proper support is determined to reach a satisfactory two-body FPA system. The nonlinearities are not considered in this study and linear Numerical models are developed using AQWA/ANSYS and Minitab software in frequency domain. Finally, a preliminary optimized model of the two-body FPA is determined in accordance with the particular sea site information of the Rio de Janeiro.Copyright

Effects of Preheat and Interpass Temperature on the Residual Stress and Distortion on the T-Joint Weld

The finite element model of ABAQUS combined with FORTRAN subroutines was developed to predict the residual stress and deformation of T-joint welds under different preheat and inter-pass temperature. A calibrated and sequentially coupled thermal and mechanical 3D finite element (FE) model is developed, and Goldak’s double ellipsoidal heat source model is implemented into the numerical model. The welding induced imperfections, including the residual stress and distortion are discussed in this paper. The results show that vertical deformation depend significantly on the preheat temperature and inter-pass temperature. The influences of preheat and interpass temperature on the residual stress are not significant.Copyright

Sandwich Pipes With Strain Hardening Cementitious Composites (SHCC): Numerical Analyses

Sandwich pipes (SP) combining high structural resistance with thermal insulation have been considered as an effective solution for using in ultra deepwater pipelines. Research has been conducted at COPPE/UFRJ with different core materials aiming to develop qualified pipes to transport deepwater oil and gas, especially for the pre-salt reservoirs in offshore Brazil. SPs using SHCC material are easy to manufacture and cost-effective. Moreover, the composition of the SHCC material can be controlled to achieve structural requirements along with good thermal insulation. Investigation on the buckling under external pressure and feasibility of installation by reel-lay method is required. This study presents numerical analysis of the collapse, collapse propagation and bending of sandwich pipes with different geometries. The Drucker-Prager formulation is employed for SHCC constitutive model and it is calibrated through small-scale tests. Model geometries match full scale specimens manufactured and tested in bending apparatus and hyperbaric chamber. Numerical/experimental correlation is also presented.Copyright

Shakedown Study of Pipes With External Corrosion Under Cyclic Bending and Internal Pressure

Pipelines and rigid risers are susceptible to corrosion. This is also a concern for pipes onshore and on process plants of floating platforms. Once detected the corrosion defect on pipes under cyclic loads, the analysis carried out to decide on keeping the pipe in operation or repair/replace should consider that the defect may experience cyclic plasticity caused by stress concentrations and thickness reductions. In this condition, ratcheting can cause rapid failure. This paper presents a study combining experiments and different analysis techniques to evaluate the occurrence of ratcheting in pipes subjected to cyclic bending and internal pressure. Experiments with different defect geometries were carried out. Numerical analysis using incremental plasticity and shakedown procedures are presented and compared with the experiments.Copyright